Influence of cooling rates on microstructure and tensile properties of a heat treated Ti_2AlNb-based alloy

摘要

In the present study, a two-phase Ti_2AlNb-based alloy with a nominal composition of Ti-22Al-25Nb (at%) comprising the dominant O + B2/β) phase was explored. The microstructural evolution and tensile properties are studied by applying different heat treatment methods of water-cooling (WC, 140 °C/s) and furnace-cooling (FC, 0.08 °C/s) after heat treatment at 1015 °C for 40 min, followed by aging treatment at 800 °C for 1, 5, and 100 h. The results indicated that the morphologies of solution-treated alloys after different cooling methods have a significant distinction. The WC alloy consists of a continuous B2/β) phase and a few remnant O phase, whereas the FC alloy comprises a mass of lath O phase and discontinuous B2/β) phase. The Widmanstatten O + B2 structures were generated in the following aging treatment. The α_2 phase was not detected during the heat treatments in the present work. The B2 phase and O phase in the aged WC and FC alloys follow the classical orientation relationship: (110)_(B2)//(001)_O. [111]_(B2)//[110]_O. The room-temperature ultimate tensile strength (UTS) and elongation to failure (EL) of the FC and aged FC alloys are higher than the WC and aged WC alloys, except for the 100 h-aging condition. On the contrary, the high-temperature UTS and EL of the aged WC alloys are higher than the aged FC alloys. The existence of the O/O phase boundaries, the coarsening of the B2 grain boundary and discontinuous precipitation harmed the performances of the studied alloys. Beyond that, the fracture mode of the explored alloys with different heat treatment methods was also analyzed.